The synthesis of acetanilide from aniline can be monitored by IR.
A number of interpreted spectra are available for interactive Jmol/JSpecView display
aniline --- acetanilide --- overlay the two --- split overlay

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The following reaction scheme has been proposed:
aniline to acetanilide white crystals of acetanilide
Some of the significant changes in the IR spectra to look for include:
the N-H region (~3400 cm-1) and the C=O region (~1730 cm-1).